This invention relates to the improved self-regulating fluid control valves, and more particularly to a self-regulating tide gate which permits reciprocal flow through a conduit connecting two bodies of water but closes to cut off such flow upon conditions which would result in an undesirably high water level in a protected one of the bodies of water.
For centuries man has tried to prevent river and tidal flooding of improved property by erecting dikes. Cross culverts or conduits are generally provided through the dikes, and one-way flap valves are installed on the conduits on the unprotected or water side of the dike to prevent interior flooding. More particularly, the one-way flap valve allows the passage of upland runoff water through the conduit, such water pushing open the one-way, top-hinged flap valve when the hydraulic head of the upland water exceeds that of the outer flood waters. As the water levels from river, estuary or ocean periodically rise, especially toward a flood level, the outer hydraulic head on the flap valve exceeds that of the interior upland water in the conduit, thereby forcing the freely pivoting top-hinged flap valve against the conduit mouth to prevent any reverse flow of water to the interior, protected area. Worldwide, this approach has been used to protect many millions of dollars of agricultural, commercial, residential, and industrial properties. But while the basic goal of flood damage protection has been achieved, the conventional one-way flap valve causes many other equally significant problems.
In tidal marsh areas adjacent to upland protected property, flood dike cross-culverts which are fitted with one-way valves exclude salt water and potential tidal ocean flooding while permitting drainage of upland runoff at low tide. But the exclusion of tidal scour and salt water also eliminates their sediment transport functions and the animal and plant life dependent upon them. Man-made and natural drainage channels fill with sediment thereby inhibiting the drainage of upland runoff which results in the increased flooding of upland storm sewers and low-lying yards and streets. As slit and debris fill in the old channels there is a concomitant increase in isolated pools of water which multiply mosquito breeding since the natural fish predators of mosquitos have been excluded with the tide. Because tidal waters are excluded, the interior water changes from salt water to fresh water, which results in the loss of salt water plants and the introduction of vigorous fresh water species such as the tall reed grass, phragmites. Phragmites grass supports artificially high tick and mosquito populations during its summer growing season and in the winter and spring its dry stems represent a severe fire and smoke hazard to improved property. Isolation of the marsh from the sea eliminates clams, shrimp, oysters, mussels and crabs. Marsh isolation eliminates all marsh-dependent fish which rely on it for breeding, nursery or feeding activities. This loss of nutrient-rich water of the healthy salt marsh short-circuits the ecological food chain to the ocean by removing its base of production. This damage to both marsh and ocean resource productivity imposes far-reaching losses to commercial and recreational fish and shellfish harvests. All of these problems can be significantly reduced or eliminated by allowing controlled salt water flushing of the marsh on the protected side of the dike if accompanied by protection against flooding improved property.
Until recently, salt water flushing without flooding has required either: (1) manually closing and opening of the simple one-way flap valve attached to a dike/conduit system during the critical discharge period before and after every storm with a flooding potential, or (2) automatic operation of relatively complex gate systems using electrical or mechanical means based on power sources external to the gate installation. Either mode of operation requires significant investment to acquire, install, operate and maintain the gate system.
In an effort to provide reciprocal water flow without flooding, Mirto U.S. Pat. No. 3,974,654 disclosed an inclined-mouth, bottom hinged, non-buoyant, float-operated valve. In operation, this valve would damage its bulkhead-dike installation and self-destruct because it failed to correctly address the need for vacuum dissipation after valve closure and thereby created more of a flooding problem than it solved. It was also unreliable in operation even prior to self-destruction.
Conventional flap valves allowing one-way flow are rarely kept in an open position because they cannot be safely closed after a significant current of water has begun to pass the valve. This is because the valve and conduit were not designed to sustain the significant forces resulting upon closure in high flow conditions, including forces due to the weight of the valve, the approach column of water abruptly stopping as it rams the face of the valve, and from the suction or vacuum pressure of the entire column of conduit water which is still moving away from the valve after it has closed.
The prior art has but one instance where reciprocal flushing without flooding has been achieved successfully, namely Steinke U.S. Pat. No. 4,091,624. The Steinke '624 patent has several gate designs all of which incorporate a vertical tube or vacuum break which dissipates the vacuum created in the cross-culvert following gate closure. However, all of the Steinke '624 patent's gate and vacuum break design are either of relatively complicated design or expensive to manufacture. Further, both Steinke's and Mirto's gates, being designed to be either fully open or fully closed, are somewhat susceptible to jamming and obstruction by ice and debris when the gate is open allowing objects to enter the mouth of the conduit.